Biexponentiality charge separation

Both the exciton/radical pair equilibrium model and the bipartite model predict formally the same kinetics and thus both give rise also to a biexponential fluorescence decay. However, the two models are fundamentally different. This difference consists in the entirely different meaning of the rate constants involved and thus in the entirely different origin of the two observed lifetimes. In the bipartite model the biexponentiality is due to the equilibration of the excitons between antenna and reaction center. Thus one of the lifetime components reflects an eneigy transfer process. In contrast to the exciton/radical pair equilibrium model the bipartite model basically describes a diffusion-limited kinetics. Despite the fact that it formaUy can describe correctly the observed kinetics, the application of the bipartite model on experimental data leads to physically unreasonable results. First it results in a charge separation time in the reaction centers which is by one to two orders of magnitude too high. 

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